An engine output control system for a vehicle for controlling engine output is already known, for example, as described in Japanese Patent Application Laid-open No. 201061/90. Such engine output control system for a vehicle electrically controls the opening and closing of a throttle valve by a drive-by-wire, for converting the target drive shaft torque of the vehicle, determined based on the accelerator pedal opening degree, into a target engine torque by use of a gear ratio of an automatic transmission and a torque ratio of a torque converter, and to open or close the throttle valve, such as, to approach a target throttle opening degree at which the target engine torque can be obtained.
In such prior art engine output control system, the throttle opening degree is indirectly determined from the target drive shaft torque and, hence, when the driver releases his or her foot from the accelerator pedal to fully close the accelerator pedal, the throttle valve does not necessarily reach a fully closed state. Thus, the fully closed position of the accelerator pedal does not coincide with the fully closed position of the throttle valve, in some cases. For this reason, when the fuel-cutting is to be conducted, for example, in the fully closed state of the throttle valve, fuel-cutting cannot reliably be achieved even, if the driver releases his or her foot from the accelerator pedal, resulting in a disadvantage that the specific fuel consumption and driveability are deteriorated.
The present invention overcomes the disadvantage that the actual accelerator opening degree does not coincide with the throttle opening degree in a lower accelerator opening degree range.
To achieve the above, there is provided an engine output control system for a vehicle for controlling engine output by electrically regulating a throttle opening degree in accordance with an accelerator opening degree, comprising: a target driving torque calculating means for calculating a target driving torque based on accelerator opening degree and vehicle speed; a target engine torque calculating means, for calculating a target engine torque, based on the target driving torque and shift position; a first output control quantity calculating means for calculating a first output control quantity of an engine, based on the target engine torque and a number of revolutions of the engine; an accelerator opening degree calculating means, for calculating the accelerator opening degree at which the target driving torque is equal to or smaller than a first predetermined value, based on the vehicle speed; a throttle opening degree calculating means, for calculating the throttle opening degree at which the engine torque is equal to or smaller than a second predetermined value, based on the number of revolutions of the engine; a second output control quantity calculating means, for calculating a second output control quantity of the engine, based on the accelerator opening degree calculated in the accelerator opening degree calculating means and the throttle opening degree calculated in the throttle opening degree calculating means; a selecting means, for selecting the first or second output control quantity, based on the target driving torque; and an engine output control means, for controlling the engine output, based on the selected first or second output control quantity.
The first predetermined value is zero, and the second predetermined value is zero.
The selecting means selects the second output control quantity, when the target driving torque is equal to or smaller than the first predetermined value.
The target driving torque calculating means calculates a target driving torque, based on the accelerator opening degree and the vehicle speed. The target engine torque calculating means calculates a target engine torque, based on the target driving torque and the shift position. The first output control quantity calculating means calculates a first output control quantity of the engine, based on the target engine torque and the number of revolutions of the engine. On the other hand, the accelerator opening degree calculating means calculates an accelerator opening degree at which the target driving torque is equal to or smaller than the first predetermined value, based on the vehicle speed. The throttle opening degree calculating means calculates a throttle opening degree at which the engine torque is equal to or smaller than the second predetermined value, based on the number of revolutions of the engine. The second output control quantity calculating means calculates a second output control quantity of the engine, based on the accelerator opening degree calculated in the accelerator opening degree calculating means and the throttle opening degree calculated in the throttle opening degree calculating means. The selecting means selects the first or second output control quantity, based on the target driving torque, and the engine output control means controls the engine output, based on the selected first or second Output control quantity.